U.S. Secretary of State John Kerry announced a ceasefire would be sought in Syria within a week and that more humanitarian aid would begin to flow into the country immediately. Declared in Munich Friday, the ceasefire would not apply to the fight against either the Islamic State group or the Nusra Front, Kerry said.

The secretary of state admitted the cessation of hostilities in Syria constituted an ambitious proposal and that there is no way to know for sure whether all of the involved combatants would honor the agreement. The humanitarian aid that world powers agreed to start providing in greater amounts would be extended to all sides in the conflict, Kerry said.

The agreement on the ceasefire was reached as Russian-backed Syrian forces are reportedly coming closer to cutting off supply lines to the city of Aleppo, a major stronghold of rebels opposed to the regime of President Bashar Assad.

Secretary of State John Kerry meets Russian President Vladimir Putin in Moscow Russian President Vladimir Putin (right) welcomes U.S. Secretary of State John Kerry during a meeting at the Kremlin in Moscow Dec. 15, 2015. Photo: Reuters/Sergei Karpukhin